1. Field of the Invention
This invention relates to a corrosion-resistant member provided with a fluorine-containing film and to a method of producing the member.
2. Description of Related Art
It has been known that corrosion-resistance of ceramics or metals against a halogen gas or its plasma is improved by forming a fluoride film, particularly an aluminum fluoride film thereon. U.S. Pat. No. 5,306,895 teaches that a aluminum trifluoride film is formed on a surface of an aluminum nitride or an alumina.
JP-A-7-273053 teaches that a surface of an aluminum member exposed to an atmosphere in a treating chamber is previously coated by replacing with fluorine. Concretely, a film of aluminum trifluoride is formed on the surface of the aluminum-based member made of alumina or aluminum nitride by introducing hydrogen fluoride, nitrogen fluoride or chlorine fluoride at 300xc2x0 C. thereinto.
JP-A-9-326384 teaches that in a plasma-treating apparatus a part of a surface of a member which is exposed to plasma is coated with a fluoride film composed mainly of aluminum. Concretely, anodized aluminum, aluminum nitride or sapphire is fluorinated to generate an aluminum trifluoride thereon. In fluorinating, at first a fluorine gas is diluted to 20-50% with nitrogen gas and the resulting atmosphere gas is pylorized at 150-400xc2x0 C. Then, in the atmosphere a sample is fluorinated by heating it to 400xc2x0 C. for two hours. Thereby, generation of particles is restrained in the treating apparatus during the plasma treating.
The inventor has made strenuous studies to give a substrate such as aluminum nitride, alumina or the like a good corrosion-resistance and to diminish generation of particles during the plasma treatment. As a result of the study, the inventor has found that merely forming a fluorine-containing film on a surface of a ceramic, such as aluminum nitride or the like, by fluorinating the surface does not highly suppress the generation of the particles. Namely, the inventor has fluorinated many substrates, which were made of aluminum nitride or alumina ceramic commercially available, by using a fluorine gas to form the fluoride-containing films thereon. However, when the resulting substrates were exposed to a cleaning gas, an etching gas or the like at high temperatures in a semiconductor-manufacturing apparatus, the generation of particles could not highly be controlled, though some degree of corrosion-resistance could be attained by the fluoride-containing film.
It is, therefore, an object of the invention to provide a corrosion-resistant member comprising a ceramic substrate and a fluorine-containing film which coats at least a part of a surface of the substrate, which has reduced a change in weight due to corrosion and at the same time a further controlled generation of particles when exposed to a corrosive halogen gas.
According to a first aspect of the invention, there is the provision of a corrosion-resistant member including a ceramic substrate and a fluorine-containing film which coats at least a part of a surface of the substrate, in which the fluorine-containing film is formed by directly contacting the substrate with a fluorine-containing compound and has a thickness of 0.01-5.0 xcexcm and the substrate contains silicon in an amount of not more than 0.5% by weight when calculated as silicon dioxide.
The inventor has found that when the fluorine-containing film is formed by directly contacting the substrate with the fluorine-containing compound and the substrate is exposed to a corrosive halogen gas or its plasma, an amount of the generated particles largely depends on the silicon content contained in the ceramic substrate, and accomplished the present invention.
Concretely, the amount of the generated particles is extremely decreased by limiting the content of silicon in the substrate to not more than 0.5% by weight when calculated as silicon dioxide. The reason is not clear but is considered as follows.
It is considered that when the ceramic is contacted with a fluorine gas at a high temperature, the silicon existing in the ceramic reacts with the fluorine to form silicon tetrafluoride. Silicon tetrafluoride evaporates to become a gas at the high temperature. For this reason, it is considered that when the amount of silicon in the ceramic is high, a fluorine-containing film is difficult to form, or even if the fluoride film is formed, the film is difficult to adhere to the surface of the ceramic substrate or the quality of the film is bad. As a result, when the resulting corrosion-resistant member is exposed to the corrosive halogen gas or its plasma, peeling of a part of the film is seen to lead to generation of particles.
In the present invention, the term xe2x80x9ca fluorine-containing filmxe2x80x9d means a film which contains fluorine in any form. The fluorine-containing film may contain nitrogen, carbon. oxygen and unavoidable impurities other than a metal element in the ceramic. The fluorine-containing film may be a film made of a fluorine-containing compound. The term xe2x80x9ca fluorine-containing compoundxe2x80x9d means a compound which contains a fluorine atom in a stoichiometric amount and involves a fluoride of a metal such as aluminum fluoride or the like.
The thickness of the fluorine-containing film is limited to 0.01-5.0 xcexcm, which is important. When it is not less than 0.01 xcexcm, the corrosion-resistance of the substrate can be ensured. From the point of view, it is preferably not less than 0.05 xcexcm.
The thickness of the fluorine-containing film is limited to not more than 5.0 xcexcm, thereby, when the corrosion-resistant member is exposed to a corrosive halogen gas, the generation of particles which is caused by the peeling off of the fluorine-containing film can be avoided. From this point of view, the thickness of the fluorine-containing film is preferably not more than 3.0 xcexcm.
For the purpose of further controlling generation of particles, the amount of silicon contained in the ceramic is preferably not more than 0.2% by weight.
The kind of the ceramic material is not particularly limited, and oxide or nitride of at least one metal selected from the group consisting of aluminum, rare earth element and alkali earth metal is preferred. Alternatively, it is preferably of double oxide or double nitride of at least two metals selected from the above-mentioned group.
The ceramic material is preferably double oxide or double nitride of aluminum and at least one of rare earth elements. In this case, since the rare earth element is also fluorinated, the resulting fluorine-containing film contains aluminum fluoride and fluoride of the rare earth element. As such a rare earth element, yttrium, ytterbium and cerium are preferable, and among them yttrium is particularly preferable.
Alternatively, the ceramic material is preferably double oxide or double nitride of aluminum and at least one of alkaline earth metals. In this case, since the alkaline earth metal is also fluorinated, the resulting fluorine-containing film contains aluminum fluoride and fluoride of the alkaline earth metal. As such an alkaline earth metal, magnesium is particularly preferable.
Particularly, the ceramic material is preferably alumina or aluminum nitride and the fluorine-containing film is preferably made of fluoride of aluminum.
Further, among oxides and nitrides of alkaline earth metals, the oxides are preferable and magnesia is particularly preferable.
Further, among oxides and nitrides of rare earth elements, the oxides are preferable. Particularly, yttria, ytterbium oxide and ceria are preferable, and yttria is particularly preferable.
A method of producing the corrosion-resistant member in the present invention is not particularly limited. As a suitable method, the following will be illustrated.
Namely, at first the ceramic substrate is prepared which contains silicon of in an amount of not more than 0.5% by weight when calculated as silicon dioxide, and then the substrate is heat-treated in an atmosphere which contains a fluorine gas of not less than 60% by volume to form the fluorine-containing film. In this case, the atmosphere preferably substantially consists of the fluorine gas. Besides, the atmosphere may contain unavoidable impurities.
The reaction is preferably conducted at a temperature range of 300-500xc2x0 C., and a partial pressure of fluorine gas is preferably 0.5-2.0 atm. The reaction time is not limited and commonly 1-10 hours.
The above-mentioned method is particularly useful for manufacturing the corrosion-resistant member in the present invention on account of the following reason. Namely, when a ceramic substrate is exposed to the fluorine gas at a high concentration, if an amount of silicon contained in the substrate exceeds 0.5% by weight when calculated as silicon dioxide, the surface of the substrate is rough because of the above-mentioned reason and formation of a high quality of the fluorine-containing film is difficult. In the producing method of the present invention, when the ceramic substrate is exposed to a fluorine gas at the high concentration, since the silicon concentration in the substrate is limited to not more than 0.5% by weight when calculated as silicon dioxide, a high quality of a fluorine-containing film can be obtained. Thereby, the amount of the particles can be decreased when the corrosion-resistant member is exposed to the corrosive halogen gas or its plasma.
Moreover, it is preferable that before the fluorinating treatment, the substrate is heat-treated in an inert atmosphere at temperatures between 100-500xc2x0 C. to remove a moisture on the surface of the substrate.
Further, after the fluorinating treatment, the substrate is heat-treated in the inert atmosphere at temperatures of 100-500xc2x0 C. or in air at 100-400xc2x0 C., thereby the fluorine-containing film can be stabilized.
The fluorinating treatment is preferably conducted by placing the ceramic substrate in a chamber, an inner surface of which is plated with Nixe2x80x94P, and introducing the fluorine gas into the chamber. It is disclosed in JP-A-9-326384 that a Nixe2x80x94P-plated chamber has a high corrosion-resistance against the fluorine gas.
Applications of the corrosion-resistant member in the present invention are not limited. Preferably, the members can be used as members at least partially contacting with the corrosive gas in a treating apparatus, for example a chemical vapor deposition apparatus, such as a semiconductor-manufacturing apparatus, a flat panel display apparatus, a hard disc-manufacturing apparatus or the like. As such a corrosive halogen gas, mention may be made of a cleaning gas such as ClF3, NF3, CF4, HF, HCl, Cl2, CxFy or the like, an etching gas, and a film-forming gas such as WF6 or the like.
As a concrete example of the corrosion-resistant member, mention may be made of a susceptor generating heat by heating with an infrared lamp, a ceramic heater, a susceptor placed on a heating surface of the ceramic heater, a susceptor embedding an electrode for electrostatic chuck therein, a susceptor embedding an electrode for electrostatic chuck and a heating resistor therein, a susceptor embedding an electrode for generating a high frequency plasma, a susceptor embedding an electrode for generating a high frequency plasma and a heating resistor therein and a shower plate.
In an apparatus for generating an excimer laser such as an excimer laser of KrF, ArF, or F2, a flange tube made of the corrosion-resistant member can be used for providing the fluorine gas or fluorine compound gas. In a luminescent lamp such as a metal halide lamp or the like, the member can be used for a corrosion-resistant member for a luminescent tube enclosing a metal halide.